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Electrostatic Machines

Until now, the most important exercise here at Niagara Science Museum was the gathering of artefacts. By now we have our hands full with apparatuses but a rather poor description of them. Give me a few weeks, we will catch-up.

Another friction

In ancient Greece, the amber was known to attract little objects after being rubbed with fur or cloth.In contact, two materials, insulating or conductive, will exchange electrons. Easiest is to "grab" electrons from air. Air is most positive; then, less positive come human skin, glass, nylon, wool, silk, cotton (not charging) Lucite has "affinity" for electrons. EDven more so: Amber, Acrylic, Nickel, Copper, Sulfur, Vinyl (PVC), Silicon, Teflon, Silicone rubber and ebonite (most negative).


The cupper disk above was acquisition as "the top plate in an electroforous machine". The insulator supposed to stick up is broken so, we will never know if the disc was used for something else. However nothing sticks out under the cupper disc and this makes it a good candidate as an electrophorus top plate.

Alessandro Volta experimented exhaustively with a capacitor invented in 1762 by Johan Carl Wilcke. Volta improved and popularized the apparatus and called it “electrophorus” The electrophorus is a manually operated electrostatic generator; understanding how it does function conducted to the invention of electrostatic machines such as the Wimshurst machine and the Van de Graaf generator. Something eludes easy understanding of how electrophorus works. I read a few "how it works" stories and in half of them apparently the author did not know what he was talking about.

Otto von Guericke (1602-1686), famous for his Magdeburg vacuum experiments, “mechanized” the amber rubbing experiment and invented the first friction electrostatic machine. A ball of sulfur was span while rubbed by hand. The sulfur charged up and the charge could be transported by Otto on a smaller conductive ball. The sulfur was found not to be essential for this experiment, the bottle in which the sulfur was formed produced almost same results, if robbed with silk or cotton. And this is how friction machine as pictured below become important research equipment in 18th century.

Franklin friction

I think that the friction machine above is made by Caspar Wistar at the specification of Ben Franklin. A prety outrageous claim! Check, please, my arguments in Franklin Wistar friction machine? and let me know what do you think. I will be thankfull even for severe criticism, if improve my understanding.

First there was the sulphur ball. Then "they" figured out that the glass bottle (in which the sulphur used to be poured in) is good enough. Ramsden replaced the bottle with a glass disk robed top and bottom, both sides, with leather pads. It worked! However, the previous owner of our Ramsden machine (above) did not really understood how important is the way one "collects" the excess charges from the glass disc and used some type of cups instead of combs. The combs, Franklin's revolutionary discovery, are easy to ignore and, by doing that, remain ignorant. Just before Christmas 2010, a beautiful Ramsden machine was sold for almost three thousand dollars on eBay. The machine was missing half the comb but was presented as complete. The lucky new owner, would be very disappointed if would try to make it work as purchased. By missing half a comb not only the charging capacity would be halved but the imbalance would make the glass disc to act as a capacitor preventing (I speculate) any collection. You lucky owner of that Ramsden machine, you owe me a beer. Actually, Ramsden owes one to Franklin…


Topler electrostatic generator


Dodd & Strthers electrostatic machine. Not to much concern with appearance but what a success it was. A cardboard house was positioned between electrodes on top of the box and set on fire by an electric discharge. The device was used to sell lightening rods!

Toepler-Holtz machine by Central Scientific Co. The fixed plate of glass has two metallic foil sectors glued onto it. The slightly-larger rotating plate has six foil dots with raised studs glued to it; the foil sectors are large enough so that two of the studs are opposite each sector




A sign of maturity for our electrostatic machines collection. Until now we did not have such an instrument. The foldable discharger is 21 inch long. The insulating handle is much to short for my comfort; a spark can jump to the holding hand before reaching for a "safer" electrode.



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